[Identification and characterization of a novel infection-related factor (cell wall hydrolase/autolysin) of Streptococcus suis serotype 2].

Streptococcus suis serotype 2 (SS2) is an economically important, zoonotic agent causing death and disease in both human and swine. According to published SS2 European strain P1/7 complete genomic sequence, primers for detection and amplification autolysin were designed. Autolysin gene was detected by PCR with genomic DNA of HA9801 (Jiangsu isolate), ZY05719 (Sichuan isolate), ATCC43765 (reference strain), other SS2 isolates from different regions, and strains of other different serotypes (such as serotype 1, 1/2, 7 and 9). PCR results showed that all 27 SS2 virulent isolates harbored gene autolysin, but not in non-virulent SS2 strain. Among other serotypes, only serotype 7 strain had this gene. The complete autolysin genes of HA9801 and ZY05719 were respectively amplified by PCR and sequenced. Their putative protein sequences were analyzed through online software, results showed both had six repeated domain GBS_Bsp-like and one domain N-acetylmuramoyl-L-alanine amidase. In addition, sequence similarity analysis demonstrated that autolysins of the two strains (HA9801 and ZY05719) showed high homologue to that of European strain P1/7 (99.8%), but obviously differed from Canada strain 89/1589, the latter lacked one domain GBS Bsp-like. Software DNASTAR was used to analyze autolysin protein sequence and predicted its putative antigenicity. Then partial antigentic segment of autolysin was amplified, cloned and inserted into expression vector pET30a(+), and induced by IPTG to express recombinant autolysin. Its reactivity was analyzed by SDS-PAGE and western blot with swine convalescent sera, blot result showed that the recombinant protein had good reactivity and could be considered as a vaccine candidate.